Wed Sep 21, 2005 12:42 pm
In my experience, the danger of fermenting with ale yeast above 70F is excess diacetyl and fruity esters, if too much higher than 75F you run the risk of increased bacteria production.
The bottom line: it depends a lot on the yeast strain your using, consult the temperature guidance given by the manufacturer. If you go any higher than that, you run a higher risk of the yeast creating off-flavors.
I recently fermented an ESB with the wyeast 1968 London ESB ale yeast at 78F slowly dropping to about 71F within the first week after transferring to the secondary. The published yeast profile from wyeast recommends fermenting at 64-72F. The yeast profile in this finished beer is very fruity and tasty, but too much diacetyl for me.. I would have been better off controlling the temp down so that fermtnation started in the low 70s at the most.